In general, a method for ray-tracing includes an Image Method and Ray Launching.
In the Image Method, when a total transmission distance of a ray is the same as a distance of a straight line from a certain point to the receiving point, the total transmission distance being a transmission distance of the ray until the ray arrives at a receiving point after being reflected from an object several times, the certain point is defined as an Image Point. The Image Method is a method of calculating a transmission distance using the defined Image Point. The Image Method is a relatively simple method to calculate the distance. However, when a complex structure that a plurality of objects are densely aggregated and scattered is analyzed, since, as an example, multiple image points may occur during a process of tracing a certain ray, there is a disadvantage that the Image Method cannot be applied.
The Ray Launching Method is a method that replaces infinite rays launched from a transmitting point with finite rays to sequentially launch the rays and traces a path of the ray until the ray is arrived at a receiving point. The Ray Launching Method may sum power of rays received at a receiving point according to traced multiple paths, and thereby can calculate a path loss or a delay dispersion and also can accurately estimate a propagation characteristic in various environment. Also, the Ray Launching Method is very useful method to estimate field strength and also to calculate the feature of the delay dispersion of a channel required to design a digital communication network. However, the Ray Launching Method has disadvantage in that a calculation thereof is complex.
Also, the Image Method and Ray Launching Method calculate each Image point and reflect point. Since a number of calculations increases as a number of objects increases, a simulation analysis rate for estimating a propagation characteristic is decreased. Accordingly, a preprocess method is applied to improve the analysis rate.
However, since current preprocess methods can calculate a reflection point or image point through a preprocess only after determining a location of a transmitting point, there is a problem in that, when the location of the transmitting point is changed even with respect to the same object, the preprocess is performed again.